Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Department name when degree awarded


Committee Chair(s)

Ting Hsiao


Ting Hsiao


Donald Davis


Neil West


The ecology, life history, and population dynamics of the sagebrush defoliator, Aroga websteri Clarke, were studied in the field and laboratory. The defoliator has one generation a year at the Curlew Valley site. It overwintered in the egg stage and passed through five larval instars. Ten parasite species attacked the defoliator at the study site . Four species, Orgilus ferus, Phaeogenes sp., Spilochalcis leptis, and Apanteles cacoeciae, contributed over 75 percent of the total incidence of parasitism. Parasitism ranged from 20 to 76 percent in 1971, but only ranged from 6 to 29 percent in 1972. This decrease in total parasitism in 1972 coincided with a five-fold increase in the defoliator population. In 1972, many mature larvae died as a result of food shortage. A microsporidian infection and a predaceous beetle also caused variable mortality during the two years. Methods for determining defoliation to sagebrush plants were also studied in the field.

The consumption and utilization of food by the fourth and fifth larval instars were determined. The fecundity, rate of development, and behavior of the insect were also investigated under laboratory conditions. Partial life tables were constructed from the findings of 1971 and 1972 to assess the r ole of various mortality factors in regulating the sagebrush defoliator numbers.



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